CN85103529A

CN85103529A - Voltage-frequency converting circuit

Info

Publication number: CN85103529A
Application number: CN85103529A
Authority: CN
Inventors: 户田政义; 浜崎诚一
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1985-05-08
Filing date: 1985-05-06
Publication date: 1986-11-05
Also published as: CN85103529B; DE3516590C2; US4672236A; CH669464A5; DE3516590A1

Abstract

One can guarantee that output frequency comprises the voltage-frequency converting circuit of the linear relationship of input voltage: a receiving inputted signal produces the input circuit that a pair of absolute value equates opposite polarity d. c. voltage signal; One is connected to the integrating circuit of capacitor in the operational amplifier negative-feedback circuit, an output circuit that produces square-wave signal, feed forward circuit on input that is connected on the non-reception integrating circuit of output circuit output signal input, and a bleeder circuit that comprises feed forward circuit.

Description

Voltage-frequency converting circuit

The present invention relates to a kind of voltage-frequency converting circuit that is mainly used in electronic power meter.

The load voltage of distribution line and power consumption electric current multiply each other by a multiplier device in electronic power meter, produce the voltage signal that is directly proportional with instantaneous power.This voltage signal is added on the voltage-frequency converting circuit, and produces its frequency by this circuit and be directly proportional with this voltage signal, i.e. the square-wave signal that is directly proportional with instantaneous power.Square-wave signal is counted so that calculate electric energy by a counter circuit, the accumulative total electric energy, and by a display unit demonstration electric energy.

In order to improve the precision of wattmeter, require voltage-frequency converting circuit in the voltage range of tens volts of non-like this constant widths, having the linear relationship of output frequency to input voltage from several millivolts.

But, when using this voltage-frequency converting circuit, because the delays in work of circuit element can produce error in high-frequency range, so that destroyed linear relationship.To do detailed explanation to foregoing according to the prior art voltage-frequency converting circuit shown in Fig. 1.

Referring to Fig. 1, a pair of input of digital 10 and 10 expressions.Between

input

10 and 10, receive as mentioned above the input voltage signal that is directly proportional with instantaneous power from multiplier device.Become a pair of d. c. voltage signal ep and en by input circuit 14 these conversion of signals, this absolute value to d. c. voltage signal equates that polarity is opposite.Input circuit 14 comprises operational amplifier 11 and resistor 12 and 13.The reversing phase switch circuit that digital 15 expressions are made of an analog switch, digital 16 expression resistors.Integrating circuit of digital 17 expressions, this integrating circuit is by constituting in the negative-feedback circuit that capacitor 19 is connected on operational amplifier 18.Output circuit 20 comprises operational amplifier 21 and

resistor

22 and 23, constitutes the hysteresis comparison circuit.More precisely, output circuit 20 produces square-wave signal a as its output signal (referring to (B) among Fig. 2), whenever the output voltage Eo of integrating circuit 17 as shown in Fig. 2 (A) reaches preset upper limit value+V _ROr reach predetermined lower limit value-V _RThe time, square-wave signal a is with regard to paraphase.Square-wave signal a is also as the signal that causes 15 actions of reversing phase switch circuit.

The operating state that foregoing circuit is arranged will be described below.When reversing phase switch circuit 15 was in operating state shown in Fig. 1, d. c. voltage signal eP was added on the negative input end 24 of integrating circuit 17, and capacitor 19 is charged.So just carry out integration, as in Fig. 2 (A) by the straight line L that descends to the right ₂Shown in, the output voltage Eo of integrating circuit 17 reduces.When output voltage Eo reaches predetermined lower limit value-V _RThe time, the square-wave signal a that produces from hysteresis comparison circuit 20 becomes logic level " 0 " as shown in Fig. 2 (B).This square-wave signal a causes that 15 actions of reversing phase switch circuit are added on the negative input end 24 of integrating circuit 17 its paraphase, d. c. voltage signal en.Therefore, just discharge of the electric charge on the capacitor 19.As in Fig. 2 (A) by the straight line L that rises to the right ₁Shown in, the output voltage Eo of integrating circuit 17 raises.Eo reaches preset upper limit value+V when this output voltage _RThe time, the square-wave signal a that produces in the hysteresis comparison circuit 20 from Fig. 1 becomes logic level " 1 " as shown in Fig. 2 (B).At this moment, cause reversing phase switch circuit 15 action by this square-wave signal a, make its again paraphase get back to original state.

When the input voltage signal e among Fig. 1 is higher, thereby the integral voltage Eo among Fig. 2 that obtains (A) just has steeper gradient.Therefore the period T shown in Fig. 2 (A) just becomes short.Because the cycle of the square-wave signal a among this period T and Fig. 2 (B) equates, so the frequency of square-wave signal a is directly proportional with the value of input voltage signal e in theory.

But, in fact exist the delay phenomenon of usually said circuit element, for example the change-over time of the input of hysteresis comparison circuit 20 and the delay between the output and reversing phase switch circuit 15 among Fig. 1, the overshoot Er shown in Fig. 2 (A) and following to Er consequently appears.The period T of integral voltage Eo just became than the time of the long 4td of true period T o like this.Therefore, the above-mentioned proportional relation between the frequency of input voltage signal e and square-wave signal a, promptly linear relationship has just been destroyed.To use mathematic(al) representation that foregoing is illustrated below.

If R ₃The resistance of expression resistor 16 is established the electric capacity that C represents capacitor 19, because the quantity of electric charge that overshoot is accumulated is:

E _r·C＝ (eP)/(R ₃) ·t _d∴E _r＝ (eP)/(CR ₃) ·t _d…（1）

Therefore, the quantity of electric charge is in one-period T:

(eP)/(R ₃) ·T＝C·（-4V _R-4E _r）

＝4C（-V _R- (eP)/(CR ₃) ·t _d）

∴｜T｜＝｜ (R ₃)/(eP) ·4C（-V _R- (eP)/(CR ₃) ·t _d）｜

Frequency f is:

｜f｜＝｜ 1/(T) ｜＝｜

\frac{eP}{{4CR}_{3} {(-V}_{R} - \frac{eP}{{cR}_{3}} {·t}_{d})}

｜…（2）

At t _d=0 o'clock, promptly under the situation that overshoot do not occur, f=(eP)/(4CR ₃) the relational expression establishment, frequency and input voltage eP(=e) be directly proportional.But, at t _d≠ 0 o'clock, above-mentioned proportional relation just no longer kept.

Make the present invention for the shortcoming that overcomes above-mentioned prior art, its objective is provides a kind of voltage-frequency converting circuit, and this voltage-frequency converting circuit just can be guaranteed the linear relationship of output frequency to input voltage by simple circuit arrangement.

Fig. 1 is the circuit diagram of a kind of prior art voltage-frequency converting circuit of expression.

Fig. 2 is the signal waveforms that is used for illustrating prior art example operating state.

Fig. 3 is the circuit diagram of expression according to a kind of voltage-frequency converting circuit embodiment of the present invention.

Fig. 4 is the signal waveforms that is used for illustrating this embodiment operating state.

In these accompanying drawings, identical mark is represented identical part or corresponding part.

Embodiment according to voltage-frequency converting circuit of the present invention has been shown among Fig. 3.In the drawings, input circuit 14, reversing phase switch circuit 15 and integrating circuit 17 are identical with circuit among Fig. 1, so no longer they are described.The invention is characterized in that resistor 40 is connected between the output circuit 20 of reversing phase switch circuit 15 and formation hysteresis comparison circuit, constitute feed forward circuit 41, the

resistor

22 and 23 of this feed forward circuit in output circuit 20 constitutes bleeder circuit.More precisely, feed forward circuit 41 is made of resistor 40, and this feed forward circuit is received on the positive input terminal 25 of reversing phase switch circuit 15 and operational amplifier 21, alternately receives d. c. voltage signal en and eP and alternately receives output signal ± E _r, and to signal en, eP and ± E _rVoltage carry out dividing potential drop, so just can keep the linear relationship of output frequency f to input voltage signal e.To use mathematic(al) representation that foregoing is illustrated below.

If R ₄And R ₅Represent the resistance of

resistor

22 and 23 respectively, establish R ₆The resistance of the resistor 40 of expression feed forward circuit 41, the voltage V on the positive input terminal 25 of operational amplifier 21 _tDefine the threshold voltage of output circuit 20, select under the situation of d. c. voltage signal eP V at reversing phase switch circuit 15 _tBe shown below:

The V in the equation (3) _tIn the substitution equation (2)-V _R:

｜f｜＝｜ 1/(T) ｜

＝｜

\frac{eP}{{4CR}_{3} (\frac{{-R}_{6} {//R}_{5}}{R_{4} {+R}_{6} {//R}_{5}} E_{s} + \frac{R_{5} {//R}_{4}}{R_{6} {+R}_{5} {//R}_{4}} eP- \frac{eP}{{CR}_{3}} t_{d})}

｜…（4）

At this moment, by selecting R ₄, R ₅And R ₆Value make equation (t _d)/(CR ₃)=(R ₅∥ R ₄)/(R ₆+ R ₅∥ R ₄) set up, following formula is then set up:

f＝ 1/(T) ＝

\frac{eP}{{4CR}_{3} (\frac{R_{6} {//R}_{5}}{R_{4} {+R}_{6} {//R}_{5}} E_{s})}

…（5）

Output frequency f just can keep and input voltage eP(=C) be directly proportional.That is to say that relation between the two is a linear relationship.From period T and true period T as shown in Figure 4 _CIt is easily that identical these actual conditions remove to understand foregoing.

When the voltage-frequency converting circuit with such good linear relation was used on the electronic wattmeter, the precision of wattmeter will improve.

On the other hand, absolute value equates that opposite polarity two voltages generate in input circuit 14 in the above-described embodiments.When input voltage satisfies these conditions, obviously can save input circuit 14.

As noted above, one is made of resistor in the present invention, and the feed forward circuit that becomes a bleeder circuit part is plugged between phase reversal switch circuit and the output circuit. Like this, even exist the work of component to postpone, also can keep reliably output frequency to the linear relationship of input voltage. In addition, because feed forward circuit is made of resistor, this just can not make whole circuit complicated, can also reduce power consumption. The voltage of the d. c. voltage signal that particularly receives by the phase reversal switch circuit in this circuit is added on the integrating circuit through dividing potential drop again, the impact that its input offset voltage of operational amplifier of formation integrating circuit causes is small, this is the advantage that this circuit has, and therefore can provide a kind of high-precision voltage-frequency change-over circuit.

Claims

A kind of voltage-frequency converting circuit comprises:

A receiving inputted signal produces the input circuit that a pair of absolute value equates opposite polarity d. c. voltage signal;

An integrating circuit that is connected to capacitor in the operational amplifier negative-feedback circuit alternately receives that to d. c. voltage signal by above-mentioned reversing phase switch circuit on its input, so that they are integrated to preset upper limit value and predetermined lower limit value;

An output circuit that produces square-wave signal, when the output signal of above-mentioned integrating circuit reached higher limit or lower limit, this square-wave signal was with regard to paraphase;

A feed forward circuit of removing that input outside the input that receives the integrating circuit output signal that is connected on above-mentioned output circuit, among the signal from above-mentioned input circuit, this feed forward circuit is by the d. c. voltage signal opposite polarity d. c. voltage signal of above-mentioned reversing phase switch circuit reception with above-mentioned output circuit;

And bleeder circuit that comprises above-mentioned feed forward circuit, this bleeder circuit the d. c. voltage signal from the d. c. voltage signal of above-mentioned feed forward circuit and above-mentioned output circuit is synthesized and dividing potential drop so that keep the linear relationship of output frequency to input voltage, and then resulting voltage is added on the above-mentioned output circuit;

Cause the above-mentioned reversing phase switch circuit of action by square-wave signal.